peterson



June 28, 1955 w. L. PETERSON 2,712,110

TAP CHANGING UNDER LOAD APPARATUS FOR QUARTER CYCLE OPERATION Filed Dec.1951 2 Sheets-Sheet 1.

awn Merv 731mm sA/g ax/cfw/o/w gm & U mum/M \N. L. PETERSCN TAP CHANGINGUNDER LOAD APPARATUS June 28, 1955 FOR QUARTER CYCLE. OPERATION 2Sheets-Sheet Filed Dec. 21,

TAP CHANGENG UNDER LOAD APPARATUS FOR QUARTER CYCLE OPERATION Walter L.Peterson, New Berlin, Wis., assignor to Allis- Chalmers ManufacturingCompany, Milwaukee, Wis.

Application December 21, 1951, Serial No. 262,868

1 Claim. (Cl. 323-435) This invention relates to voltage regulatingsystems including regulating transformers having tap changing apparatusdesigned for operation While the regulating transformer is under load.The invention is particularly related to improvements in the tapchanging circuit for such regulating transformers.

The tap changing under load apparatus of voltage regulating transformersare a considerable factor in the determination of the maximum ratingsfor which such transformers can be designed, and may even be thedetermining factor of the maximum rating of the regulator. Because theswitching apparatus of such tap changers must operate under load thereare practical limitations of their current ratings, and theselimitations therefore aifected the size and rating on the regulatingtransformers.

The invention hereinafter described comprises a new under load voltageregulating system in which the number of regulating steps may be doubledand in which the current rating of the tap changing apparatus isconsiderably increased independently of the type of regulatf ingtransformer or the type of tap changing apparatus associated with theregulator. While the invention is adaptable to and described withrelation to regulators embodying dial switch tap changing apparatus, itis not limited to such apparatus.

It is an object of the present invention to provide a circuit forreducing the current carried by the tap changing apparatus of step typevoltage regulators.

Another object of this invention is to provide an improved circuit forstep type under load voltage regulators in order to have a minimumcurrent carried by the individual elements of the tap changingapparatus.

Still another object of this invention is to provide an improved currentdividing circuit for the tap changing apparatus of voltage regulatorshaving either half cycle or quarter cycle step regulation.

It is a further object of this invention to provide a circuit by whichthe current carried by the contacts of tap changer apparatus of steptype voltage regulators is reduced and by which the number of regulatorsteps can be doubled by providing quarter cycle step regulation.

Objects and advantages other than those above set forth will be apparentfrom a consideration of the following description when read inconnection with the accompanying drawings, in which:

Fig. 1 is a diagram of a circuit for a step type voltage regulatorembodying this invention, with the regulator shown in a fully cycleposition;

Fig. 2 is a diagram of the regulator of Fig. l in a half cycle position,and

Fig. 3 is a diagram of the regulator of Fig. l in a quarter cycleposition.

The voltage regulator illustrated in the drawing is a step typeregulating transformer usable for maintaining voltage of a load circuit8, 9 at a constant value independently of changes in the load. In thisinstance.

nited States Patent 0 2,712,110 Fatented June 28, 1955 the regulatorincludes an exciting winding 11 which has a plurality of spaced taps 12to 19 and dial type under load tap changing equipment 30 with which theload circuit is regulated by changing the position of load line lead orregulator terminal 9 at the taps of the winding 11 through the tapchanging equipment. Operation of the dial switch tap changing equipment30 is accomplished through driving gears 29 by a motor 48, which can becaused to operate in either of two directions by switch 49 connectingthe motor to its source 47. Operation of the motor in one directionraises the load voltage, and operation of the motor in the otherdirection lowers the load voltage. Conventional, automatic controlmechanism (not shown) may be provided so that the switch 49 responds tovoltage changes of the load circuit.

in the dial switch tap changing equipment illustrated there is embodieda pair of tap changing apparatus, each of which includes a pair ofmovable contacts and a preventive autotransformer. in one of the tapchanging apparatus there is an autotransformer 51 which has one of itsterminals connected to movable contact 33,

through collector ring 44 and which has the other of its terminalsconnected to movable contact 34 through collector ring 42. The other tapchanging apparatus includes autotransformer 52 which has one of itsterminals connected to collector rings 43 and to movable contact 35. Theother terminal of the autotransformer 52 is connected to collector ring41 and movable contact 36. All the movable contacts, 33, 34, 35 and 36,preferably are moved substantially simultaneously by common meansincluding a motor 48 and gear drive 29. However, the four movablecontacts do not all have to be moved simultaneously nor does the tapchanger have to be a dial switch. In fact, conventional cam operatedcontactors may be utilized as tap changers.

The preventive autotransformers 51, 52 have midtaps 61 and 62,respectively. One terminal of a paralleling reactor 53 is connected tomidtap 61 and the other terminal of the reactor 53 is connected tomidtap 62, and the midtap 63 of the reactor 53 constitutes the terminal9 of the system.

The tap changing equipment has fixed contacts which with the movablecontacts preferably are arranged to make a dial type switch. Pairs ofthe fixed contacts are severally connected to the taps of the winding,such as the pair of contacts, 21 and 22, which are electricallyconnected to tap 14 of the winding 11. The fixed contacts are mounted onan insulating board 37. The pairs of fixed contacts associated with thespaced taps of the winding are supported in circumferentially spacedrelation relative to each other. in the preferred form, the contacts ofeach of the pairs of movable contacts, 33, 34 and 35, 36, are spaced tocoordinate with the circumferential length of the fixed contacts andwith the circumferential spacing between adjacent fixed contacts so thatthe contacts of each pair of movable contacts may both be on one fixedcontact in a full cycle position (Fig. l) and so that they may bridgeadjacent of the fixed contacts as shown in Figs. 2 and 3, in half cycleor quarter cycle positions, respectively.

The embodiment of this invention for under load regulators providescurrent division to the four movable contacts for full and half cyclestep type regulation, thereby making it possible to avoid some of thelimitations imposed upon regulating transformers by their tap changingequipment.

In operation, the load current is always divided equally to each of themovable contacts of the tap changing equipment. In the full cycleposition the load current at the system terminal 9 is caused to divideequally by the midtapped paralleling reactor 53 with conductors 54, 55carrying one half load current. The midtapped preventiveautotransformers 51, 52 divide current equally to the conductors 5e, 57,58 and 59 which are connected between terminais of the autotransformersand collector rings 41, 42, 43 and 44 so that one fourth load current isin each of the four circuits to the four collector rings and to themovable contacts 33, 34, 35 and 36.

Fig. 2 shows the equipment in a half cycle position, and it is evidentthat the load current from terminal 9 is divided by the parallelingreactor 53 between. the conductors 54, 55 which are connected to theterminals of reactor 53. The-current is again divided by the midtappedautotransformers 5i and so that only one fourth load current is carriedin each conductor 56, 57, 53 and 59, in each collector ring and in eachmovable contact. With one of the preventive autotransformers 51connected between the contacts 33, 34 of one pair of movable contactsand with the other preventive autotransformer 52 connected between thecontacts of the other pair of movable contacts, the bridging position,either half cycle or quarter cycle, is effected with the preventiveautotranstormers limiting the circulating current through theautotransformers to an inappreciable amount.

With the improved circuit illustrated in the draw lugs and describedabove, quarter cycle operation of the step type regulator may beeffected, thereby doubling the number of regulating steps whilemaintaining even step regulation through the entire regulating range ofthe equipment.

For quarter cycle operation, only one connection from the taps of thewinding to the terminals of the midtapped autotransformers is changedduring each operational step. When dial switches are utilized as in theillustrated embodiment, such regulation is accomplished by spacing andarranging the movable contacts with respect to each other and withrespect to the spacing between adjacent fixed contacts so that a singleregulating step operation involves the movement of only one movablecontact from one fixed contact to an adjacent fixed contact. The spacebetween the adjacent movable contacts is slightly greater than the spacebetween adjacent fixed contacts, and as soon as one movable contactmoves ofi or one fixed contact and on to an adjacent fixed contact, thetap changer mechanism is stopped.

The improved regulating system functions substantially in the samemanner with the regulator in a quarter cycle position as with theregulator in a half cycle position. In either position, there is currentlimiting means in the form of a preventive autotransformer connectedbetween the contacts of the pair of movable contacts that bridgeadjacent taps of the Winding. Also, there is only one quarter loadcurrent at each movable contact because of the current dividing meansprovided by the midtapped reactors.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to one skilled in the artthat various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claim.

Features disclosed but not claimed herein are claimed incopendingapplication Serial No. 262,785 of Louis C. Aicher, filedDecember '21, 1951, for a Tap Changing Under Load Apparatus WithParalleling Reactors Common to All Taps.

It is claimed and desired to secure by Letters Patent:

A voltage regulating system comprising a system terminal, a transformerhaving a winding with a plurality of taps and tap changing apparatusincluding a dial switch mechanism having a plurality of fixed contactsseparately connected to said taps with said fixed contacts disposed incircumferentially spaced relation to each other, first and secondpreventive autotransformers, a midtapped paralleling reactor, fourmovable contacts cooperative with said fixed contacts to vary theconnection of said terminal to said winding, said first preventiveautotransformer connected between two of said movable contacts, saidsecond preventive autotransformer connected between the other two saidmovable contacts, said first autotransformer having a midtap connectedto one terminal of said reactor, said second autotransformer having amidtap connected to the other terminal of said reactor, the midtap ofsaid reactor constituting said system terminal, and common means to movesaid movable contacts to alternately connect all of said movablecontacts to any single one of said taps of said winding and move saidmovable contacts one at a time from connection with said any single oneof said taps to connection with an electrically adjacent said tap tocause the voltage at said system terminal to vary in steps equal to onefourth the voltage between said single tap and said adjacent said tap.

"Railway Electrical Engineer, September (pages 188 and 189 relied on).

Electrical Engineering, October (pages 727732 relied on).

1942, vol. 61

